When you say "on the cylinder", do you mean on the face of the cylinder, like this
or do you mean on the crane, like this?
If on the face, that should be the SN of the gun, so your cylinder has been replaced. If on the crane, that's an assembly number, and has nothing to do with the SN.
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.